“Their legal careers, and by extension their marriage, are the stuff of lore. Mary Jo White leads the Securities and Exchange Commission; her husband, John, practices law at an old-guard firm as elite as the corporations it represents. Together, they are a legal power couple that straddles Wall Street and Washington like few others.

“Their careers, however, can at times collide, generating headaches for the S.E.C. as it pursues wrongdoing in the nation’s financial markets, according to interviews with lawyers and a review of federal records. In the nearly two years since Ms. White took over the agency, she has had to recuse herself from more than four dozen enforcement investigations, the interviews and records show, sometimes delaying settlements and opening the door, in at least one case, to a lighter punishment.”